Spectroscopy relates to absorption and emission of light, particularly as it relates to wavelength of the light. Natural light is composed of many colors in a spectrum. Often, it is necessary to analyze the spectrum to determine characteristics of the source of light. In use, spectroscopy requires that a source of light be dispersed so that different wavelengths of light are transmitted differently. A detector senses presence of light where it appears after dispersion and determines characteristics of the light. Various methods have been used to disperse the spectrum, including use of a prism or a diffraction grating. A prism disperses the light into its component colors using refraction. The diffraction grating includes a plurality of closely spaced slits on a flat surface.
In one particular form of a spectrometer, based on the Rowland circle principle, a circular chamber is provided. Light from a source is directed through a lens into an entrance slit in the chamber so that it is directed at a concave grating. The grating lies on a circumference of the circle. The diameter of the circle is equal to the radius of the curvature of the grating. As a result, the light is diffracted and imaged onto an arc of the circle.
In a particular application, the Rowland circle type spectrometer is used to observe discrete wavelengths or spectral regions of a sample. The sample is present in the light source. As a result, the light source has spectral characteristics depending on the presence or absence of the sample. An exit slit is provided in the circle so that light having a specific wavelength within the spectrum will exit the exit slit. The amount of light can be sensed by a detector such as a photomultiplier tube. This device is used to detect the presence of the sample in the light source based on the intensity at the particular wavelength being above a select level corresponding to the sample.
One problem with a conventional spectrometer as discussed above is that the light source often consists of a hot flame with a different type of gas. Flickering of the light causes problems due to constant changes in intensity. A small amount of the sample may be hard to distinguish from flickering. In prior devices, this problem has been solved by looking at the wavelength of interest relative to a closely related wavelength. The intensity of the two wavelengths are compared to determine the presence of the particular sample. This is often done using glass or quartz in the light path which is mechanically moved back and forth to shift the light so that the light sweeps past the exit slit. If the signals are different, then this indicates the presence of the sample. To be effective, though, the mechanical movement must be faster than natural fluctuations due to flicker and the like. However, quartz or glass tend to be quite heavy, rendering such mechanical movement difficult to achieve.
The present invention is directed to overcoming one or more of the problems discussed above in a novel and simple manner.